1. Field of the Invention
The present invention relates to a composition for stripping and a stripping method, and more specifically, a composition and a method for easily stripping a color resist or organic insulating film formed on a substrate for reuse of the substrate when defects occur during a process of forming the color filter or organic insulating film on the substrate.
2. Description of the Related Art
In a liquid crystal display device, a top substrate includes: red, green and blue color filters; a black matrix for preventing light leakage between each pixel and improving contrast ratio; and a common electrode for applying a voltage to liquid crystal cells.
A process of manufacturing the color filter on the top substrate is as follows. Cr/CrOx or an organic material that is used as a material for the black matrix according to its use is applied on a glass substrate to form a pattern. A black mask pattern is formed. Thereafter, a color resist pattern is formed by a photolithography technique in order to display colors. The color resist is applied on the glass substrate, and exposed to be cured by photopolymerization. After exposure, the unexposed region of the color resist is removed by development, and the color resist goes through a baking process.
The color resist is produced by a pigment dispersion method, a dyeing method, an electrodeposition method or the like, and the pigment dispersion method is frequently used. The organic pigments to display colors are generally dispersed in a photosensitive composition for photoresist including a photopolymerization initiator, a monomer, and a binder. The photopolymerization initiator is a highly sensitive compound capable of generating radicals when irradiated. The monomers form a polymer by radicals after the initiation of polymerization reaction and become insoluble in the solvent. The binder protects the liquid monomers from a developer at room temperature, and affects stability of pigment dispersion, and reliability of heat-resistance, light-resistance, and drug-resistance of red, green, and blue patterns.
Until now, once the color resist is cured during the process of manufacturing the color filter, it is impossible to remove or repair only the defective portion of the pattern. Further, since there is no appropriate solvent to remove the color resist, the substrate on which the defective color filter is formed has been discarded.
The color resist is a negative type resist, which is typically difficult to remove by stripping as compared to a positive type resist, thereby making desirable an improved stripping performance.
Specifically, in a case where the color filter is formed on a thin film transistor of a bottom substrate, an electrode formed of a metal including Al can be damaged during removal of the color resist. Thus, the stripping performance to solve these problems has been demanded.
In addition, an appropriate stripping composition capable of removing the negative type organic insulating film formed on the thin film transistor is not well established presently, which increases demand for a composition capable of stripping the films.
For the reasons described above, an inorganic stripping solution and reactive ion etching (RIE) using plasma have been conventionally used. However, to use the inorganic stripping solution, sulfuric acid, nitric acid, fuming sulfuric acid, and a mixed solution of nitric acid and hydrogen peroxide are heated to 120° C. or more, which requires the greatest caution while handling to ensure the user's safety and to avoid risk of fire.
An RIE method using plasma for removing a cured color resist, which is hardly removed by a conventional wet etching method, is disclosed in U.S. Pat. No. 5,756,239, in which O2-RIE and SF6-RIE are used continuously. Further, a method of removing an absorption layer of a color resist by plasma using oxygen and removing a barrier layer of a color resist by RIE using sulfur hexafluoride or nitrogen trifluoride is disclosed in U.S. Pat. No. 5,059,500, in which polyester, polyamide, and novolac resin are used as an absorption layer and polysilane, polysiloxane, an organosilicon compound, silica, silicon nitride and mixtures thereof are used as a barrier layer. However, the method of etching the color filter by using plasma has practical limitations because it requires high vacuum and high energy, the control over process conditions is difficult, the method can not be used for a wide area, and expensive equipment is used.
As such, a large amount of color resist cannot be easily removed by conventional methods due to concern over user safety and decreased productivity and yield.